Without limiting the scope of the invention, its background is described in connection with spinal fixation assemblies to align vertebral bodies, as an example.
The successive positioning of the vertebral body allows the vertebral foramen to surround the spinal cord, retain articulation of the vertebrae and extend posteriorly of the spinal canal. The complicated vertebral structure, the degree of spinal articulation and the complicated network of connective elements make the spine susceptible to many forms of damage, e.g., traumatic spinal injuries, tumors, infections, surgeries, disease processes, aging processes and congenital abnormalities. Various types of spinal column disorders are known and include degenerative disc disease, excess lordosis (abnormal backward curvature of the spine), fractured vertebra, kyphosis (abnormal forward curvature of the spine), ruptured discs, scoliosis (abnormal lateral curvature of the spine), slipped discs, spondylolisthesis (abnormal forward displacement of vertebra) and the like.
Bones may be damaged (i.e., fractured) as a result of accidents (e.g., long bone fractures being the most common) or severed during a surgical procedure. The bone portions must be held together and stabilized from movement to allow bonding and recalcification. Due to the variation in the size, shape and location of the bone and to account for different function and load requirements, many different types of stabilization devices have been developed. In order to limit the movement of the bone plates, screws and pins are often used. Common internal fixation devices include wires, intramedullary pins, rods, wiring, plates, screws, bone fasteners and elongated implants (e.g., nails, screws, pins, etc.). Bone fasteners are commonly used to stabilize portions of the spine. Bone fasteners are inserted in the pedicles of a vertebra and used in conjunction with rods or plates to stabilize the spine. Generally, an incision into the tissue surrounding the bone and the bone portions are clamped together so that holes may be drilled into the bone. Pins or screws are then inserted through the holes to secure the bones. A cast or splint is added to further reduce the movement and mechanical strain on the bone that may cause bone separation.
Generally, spinal fixation assemblies are used to position the vertebrae in a desired spatial relationship for treatment, e.g., healing, spinal fusion, support and so forth. Spinal fixation assemblies include spinal fixation elements commonly anchored to the vertebrae via pedicle screws that extend through the pedicle into the vertebral bodies or by spinal hooks that engage about the vertebrae. The spinal fixation elements are coupled together with relatively rigid fixation rods by generally yoke-shaped couplers that can be either integral with the spinal fixation element or separate components from the spinal fixation element. The spinal fixation elements are secured relative to the fixation rod by a compression member that is engages either directly or indirectly the fixation rod. The fixation rods are secured to maintain the alignment and position of the vertebral bodies.
For example, one such method of orthopedic fixation is taught in U.S. Pat. No. 5,005,562 issued to Cotrel, and incorporated herein by reference, which teaches an implant for a spinal osteosynthesis device, in particular in traumatology. The implant includes a body having a channel defining two side branches that are open on both sides of the body in order to be able to receive a rod, and a threaded plug contrived so that it can be screwed into a female thread formed in the inner walls of the two branches so that its two diametrically opposed edges bear on the rod and the face of the plug directed towards the rod, which can thus be clamped in translation and rotation.
Another such method of orthopedic fixation is taught in U.S. Pat. No. 6,623,485 issued to Doubler, et al., which teaches a split ring bone screw for a spinal fixation system. The adjustable spinal fixation system includes anchoring assemblies attached to spine-stabilizing rods. The anchoring assemblies include a linking member attached in a ball-and-socket fashion to a bone-engaging member that is adapted to engage a spinal bone of a patient. The linking member joins one of the included connectors to an associated bone-engaging member. The connectors are attached selectively to one of the stabilizing rods. The anchoring assemblies each include a support collar and a split retention ring that cooperate to allow adjustment of the bone-engaging member and corresponding connector during surgery. When surgery is complete, a securing nut and locking bolt cooperate with the support collar and split retention ring to maintain the relative position of the entire fixation system, preventing unwanted movement between the system components.
An orthopedic fixation is taught in U.S. Pat. No. 6,610,063 issued to Kumar, et al., which teaches a spinal fixation system that is particularly useful in treatment of pediatric and small-statured patients. The fastener assembly includes a fastener, an attachment member and a locking member. The fastener has a lower portion for contacting a bone and an upper portion integral with the lower portion and having two open channels. Each channel is configured and dimensioned for receiving a portion of the longitudinal member along its circumference. The attachment member is positionable on the fastener and at least partially covers the channel that receives the longitudinal member. The attachment member is configured and dimensioned for receiving another portion of the longitudinal member along its circumference. The locking member is operatively associated with the upper portion of the fastener and secures the attachment member and longitudinal member to the fastener.
Another such method of orthopedic fixation is taught in U.S. Pat. No. 6,945,975 issued to Dalton, which teaches a bone plate for fixation of spaced vertebra. The bone plate has at least one through passage for securing the plate to bone with a bone fixation screw. The threaded shaft of a bone fixation screw is inserted through a bushing located in the through passage of the bone plate and the screw is thereby threadably secured to the underlying bone. Next, the bushing is compressed inward against the head of the screw with cams that are actuated by rotating the bushing in the through passage, whereby the screw is locked relative to the bone plate. The bushing is not only compressed inwardly against the head of the screw but is also compressed downwardly by the cams into a seat to clamp separate elements of the bone plate together.
Another approach is the orthopedic fixation taught in U.S. Pat. No. 6,248,106 issued to Ferree, which teaches a spinal stabilization mechanism that acts to prevent lateral bending, extension and rotation at the disc space. The patent teaches two or more anchors at each vertebral level and links at each vertebral level to both anchors at the other vertebral level resulting in a cross-braced arrangement that enhances compression and promotes fusion.
In addition, a flexible stabilization system for a vertebral column is taught in U.S. Pat. No. 4,743,260, issued to Burton, which teaches a device that includes a strong, non-metallic stabilization element or elements for providing flexibility. The stabilization elements are secured to the vertebrae to stabilize the vertical column while still allowing for flexibility. The stabilization elements are anchored to the vertebrae by a bone screw having an upper shank portion and a lower threaded portion having a segmented area.
In some instances, there is a need for a spinal fixation assembly that provides a stronger and/or more stable spatial relationship for the vertebrae. For example, a dual fixation rod assembly can be both strengthened and stabilized by the addition of a cross-brace that extends across the spine to couple the two fixation rods. This is seen when the two fixation rods are geometrically aligned, i.e., the two rods are parallel. However, in clinical situations, the two fixation rods are rarely three-dimensionally geometrically aligned and are bent to accommodate the alignment, e.g., bending one or both of the two fixation rods and/or the cross-brace. The bending can adversely affect the fixation to the spine and adversely affect the mechanical properties of the fixation rods and/or cross-brace. Given the constrained size limitations imposed by the spinal area and the size and strength necessary for the spinal fixation assemblies, the alignment of non-coplanar rods, convergence alignments, divergence alignments and augmented spinal fixation assemblies is difficult.
The foregoing problems have been recognized for many years and while numerous solutions have been proposed, none of them adequately address all of the problems in a single device.